Problem: Expand.
Solution: $\begin{aligned} ( x{-1})(x+4)&= x(x+4){-1}(x+4) \end{aligned}$ $\begin{aligned} \phantom{( x{-1})(x+4)}&=x^2+4x-x-4 \\\\ &=x^2+3x-4 \end{aligned}$